Function d_quat_chunk 

fn d_quat_chunk<B: Backend>(
    states_bhlpr: &F<B, 5>,
    d_phys_bhlpr: &F<B, 5>,
    blocks: usize,
) -> F<B, 5>

The per-block quaternion gradient of the de-rotation (c = Q ⊗ h̃ ⇒ d_Q = Σ_p d_c ⊗ conj(h̃)).